EGU25-11037, updated on 15 Mar 2025
https://doi.org/10.5194/egusphere-egu25-11037
EGU General Assembly 2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
Atmospheric Rivers and Compound Inland Flooding under Climate Change
Mohammad Reza Najafi1, Mohammad Fereshtehpour1, Andrew Grgas-Svirac1, and Alex Cannon2
Mohammad Reza Najafi et al.
  • 1Western University, Civil and Environmental Engineering, Canada (mnajafi7@uwo.ca)
  • 2Climate Research Division, Environment and Climate Change Canada, Canada

Compound Inland Flooding (CIF) arises from the interactions between multiple hydrometeorological drivers, often magnified by landfalling Atmospheric Rivers (ARs) along the Pacific Northwest coast and interior basins of North America. This study investigates the mechanisms behind two primary CIF types, Rain-on-Snow (ROS) and Saturation Excess Flooding (SEF), using the CanRCM4 large ensemble under global warming levels of +1.5°C, +2°C, and +4°C. By examining the joint occurrence of ARs with ROS and SEF across key sub-regions, including the Cascade Range, Sierra Nevada, and the Great Lakes Basin, we assess the probabilities, seasonal shifts, and hydrological impacts of CIFs in the 21st century. Results show distinct regional patterns, with ROS events projected to decrease in frequency across the Pacific Northwest and Great Lakes Basin but remain significant in high-elevation regions prone to seasonal snowmelt, such as the Canadian Rockies. Conversely, SEF events are projected to increase substantially, particularly in the eastern U.S. and southern Great Lakes, driven by intensified precipitation and persistently saturated soils. The findings indicate that under higher warming levels, the contribution of ROS to extreme runoff can decrease, while SEF-driven flood events become dominant. Signal-to-noise ratio analysis shows that internal climate variability contributes considerable uncertainty to CIF projections in transitional climate zones but is overshadowed by external climate forcing at higher warming levels, particularly in coastal regions. By capturing the compounded effects of precipitation extremes, snowmelt dynamics, and soil moisture conditions, this study underscores the necessity of integrating AR-driven compound events into regional flood risk management strategies. 

How to cite: Najafi, M. R., Fereshtehpour, M., Grgas-Svirac, A., and Cannon, A.: Atmospheric Rivers and Compound Inland Flooding under Climate Change, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11037, https://doi.org/10.5194/egusphere-egu25-11037, 2025.